1. Technical Field of the Invention
The present invention relates to infrared sensors, in particular, to an infrared sensor provided with a diaphragm structure.
2. Description of the Related Art
A known infrared sensor as a background of the present invention is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 5-172629. In FIGS. 5 and 6, a known infrared sensor 1 includes a diaphragm 3 supported by a substrate 2. The diaphragm 3 is a member having a heat-insulative structure. The diaphragm 3 is provided with an infrared detector 4 including a thermistor and the like. The infrared detector 4 is disposed on the diaphragm 3 so that the range of temperature-rise in the infrared sensor is enlarged, thereby improving sensitivity and responsiveness in the infrared detection. The infrared sensor 1 is characterized in that each peripheral side of the infrared detector 4 formed in a rectangle in plan view is set to approximately ⅔ of the length of each side of the diaphragm 3 which is rectangular in plan view, in order to enlarge the range of temperature-rise in the infrared detector 4 by avoiding heat transmission from the diaphragm 3 to the supporting substrate 2, in which the area of the infrared detector 4 is approximately 44% of the area of the diaphragm 3.
However, in the infrared sensor 1, the amount of heat diffusing to the outside air in contact with the diaphragm 3 is larger than the amount of heat which is transmitted to the supporting substrate because the diaphragm 3 is thin and the thermal conductivity is low. Therefore, the output voltage of an infrared sensor may be triplicated when vacuum level is increased and the amount of heat diffusing to the outside air is thereby reduced, as shown in FIG. 7. In such infrared sensor, an optimum value cannot be obtained when the ratio of the length of a side of the infrared-absorptive film to that of the diaphragm is ⅔, whereby it is difficult to obtain a sensor having a large output and high sensitivity.
Accordingly, an object of the present invention is to provide an infrared sensor having a large output and high sensitivity.
An infrared sensor according to one aspect of the present invention comprises a substrate; a diaphragm supported by the substrate; at least one thermocouple provided with a cold junction formed on the substrate and a hot junction formed on the diaphragm; and an infrared-absorptive film formed on the diaphragm so as to cover the hot junction of the thermocouple. The area of the infrared-absorptive film is 64% to 100% of the area of the diaphragm.
An infrared sensor according to another aspect of the present invention comprises a substrate; a substantially rectangular diaphragm supported by the substrate; at least one thermocouple provided with a cold junction formed on the substrate and a hot junction formed on the diaphragm; and a substantially rectangular infrared-absorptive film formed on the diaphragm so as to cover the hot junction of the thermocouple. The length of a side of the substantially rectangular infrared-absorptive film is from 80% to 100% of the length of the side of the diaphragm.
An infrared sensor according to a further aspect of the present invention comprises a substrate; a substantially circular diaphragm supported by the substrate; at least one thermocouple provided with a cold junction formed on the substrate and a hot junction formed on the diaphragm; and a substantially circular infrared-absorptive film formed on the diaphragm so as to cover the hot junction of the thermocouple. The inner diameter of the substantially circular infrared-absorptive film is from 80% to 100% of the inner diameter of the diaphragm.
With the arrangements described above, the diffusion of the heat from the diaphragm to the outside air can be suppressed. The amount of heat received at the diaphragm can be increased by increasing the area of the infrared-absorptive film, thereby enlarging the range of temperature-rise in the diaphragm, whereby an infrared sensor having a large output and high sensitivity is obtainable.
The object described above, further objects, features, and advantages of the present invention will become more apparent from the following description of embodiments according to the present invention with reference to the drawings.